mail: stop using the smtplib.SSLFakeFile and use socket.socket.makefile

They're equivalent, and the latter is what Python 3.3 says to use in
the release notes. Turns out it works on Python 2 as well.

Differential Revision: https://phab.mercurial-scm.org/D3956

mercurial/mail.py

@@ -79,7 +79,7 b' class SMTPS(smtplib.SMTP):'
                                         self.keyfile, self.certfile,
                                         ui=self._ui,
                                         serverhostname=self._host)
-        self.file = smtplib.SSLFakeFile(new_socket)
+        self.file = new_socket.makefile(r'rb')
         return new_socket
 
 def _pyhastls():